1. Field of the Invention
This invention relates to terminal block assemblies of the type including a plurality of electrically isolated sections, each having a terminal located therein. In particular, the invention relates to terminal block assemblies having dead-front protection. With this type of protection the terminals located in the sections are at least partially covered, so that shock and short circuit hazards are minimized. Such protection is not only desirable but, for certain applications, is required under UL Standards in the United States and under VDE Standards in Western Europe.
2. Description of the Prior Art
A portion of a conventional dead-front terminal block assembly is illustrated in FIG. 1. This terminal block assembly consists of a one piece insulating molding 10 having a plurality of hollow sections 12, each containing a tubular clamp terminal 14. Each terminal comprises a tubular conductor 16, open at both ends, a pair of clamping screws 18 mounted in respective threaded holes formed in one side of the tubular conductor adjacent the open ends, and a clamping strap 20 passing through the tubular conductor near the side having the threaded holes. Each section 12 of the insulating molding 10 has openings 22 at opposite ends providing access to the opposite ends of the tubular conductor 16 located in the section for enabling the insertion of wires or other conductive elements which are to be electrically-connected to each other by the tubular conductor. The insulating molding 10 also includes hollow extensions 24 for enclosing the heads of the clamping screws 18. The end of each hollow extension has an access opening 26 for inserting a screwdriver or test prod. The screws 18 mounted in each tubular conductor are turned after insertion of wires (not shown) into opposite ends of the tubular conductor, forcing the ends of the respective clamping strap 20 against the wires to clamp them in place.
In dead-front terminal blocks such as that shown in FIG. 1, access to the terminals and the clamping screws is restricted, but none of the openings providing access are covered as is sometimes desired. For example, it is sometimes necessary to mount a terminal block with one side in close proximity to circuitry, such as on a circuit board itself, with one side abutting circuitry on the board. In this case, it is desirable to cover the side of the terminal block to provide an effective barrier against short circuits, while still enabling connection of selected terminals to the circuitry. Also, the type of terminal block shown in FIG. 1 is limited to a specific type of tubular terminal, and cannot accept many of the terminal types commonly used with terminal blocks. For example, right angle feed-through terminals cannot be inserted through the small openings in the terminal block. Additionally, it is difficult to assemble the tubular terminals used, because the clamping screws cannot be mounted in the threaded holes of the tubular conductors until both the clamping screws and the tubular conductors are inserted into the hollow sections. After insertion, the ends of the screws must be aligned with the threaded holes, while both are hidden from view by the insulating block material.
Terminal blocks which are suitable for mounting on circuit boards in close proximity to circuitry are disclosed in U.S. Pat. Nos. 3,904,266 and 4,099,826. The terminal blocks disclosed in these patents each comprises a block of insulating material having a base portion in which are mounted a plurality of terminals separated by molded barriers defining individual sections of the terminal block. A molded wall is provided at the back of each section to serve as a protective barrier against electrical contact with circuitry or other conductive elements located behind the wall. The back walls include respective openings to facilitate the electrical connection of conductive elements located behind the walls to the terminals in the sections, but specially-shaped feed-through terminals with deformable contact elements must be used. Besides this limitation, no means is provided for providing dead front protection at the front or top sides of the terminals.
Terminal blocks having covers on their top sides are disclosed in U.S. Pat. No. 4,180,305, which has the same inventors as the present application, and in U.S. Pat. No. 3,247,480. Each of these terminal blocks includes a cover which snaps over the top of barriers between adjacent terminals. The cover is pivoted away or removed from the top side of the terminal block to gain access to the terminals. Protection will be lost, however, if the cover is misplaced, and no means is provided for closing the front or back side of the sections.